The binding of lanthanide containers [Ln(-diketonate)3dig] (dig = 1-methoxy-2-(2methoxyethoxy)ethane) to aromatic tridentate N-donor ligands (L) in dichloromethane produces neutral nine-coordinate heteroleptic [LLn(-diketonate)3] complexes, the equilibrium reaction quotients of which vary with the total concentrations of the reacting partners. This problematic drift prevents the determination of both reliable thermodynamic stability constants and intrinsic host-guest affinities. The classical solution theory assigns this behavior to changes in the activity coefficients of the various partners in non-ideal solutions and a phenomenological approach attempts to quantitatively attribute this effect to some partition of the solvent molecules between bulk-innocent and contact-non-innocent contributors to the chemical potential. This assumption eventually predicts an empirical linear dependence of the equilibrium reaction quotient on the concentration of the formed [LLn(-diketonate)3] complexes, a trend experimentally supported in this contribution for various ligands L differing in lipophilicity and nuclearity and for lanthanide containers grafted with diverse beta-diketonate co-ligands. Even if the origin of the latter linear dependence is still the subject of debate, this work demonstrates that this approach can be exploited by experimentalists for Introducing eqn (4) into eqn (2) yields eqn (5) where ,M 1,1,eq Q L is the experimentally accessible reaction quotient, which is (very) often mistaken by coordination chemists for the thermodynamic stability constant ,M 1,1

Access to reliable values of the thermodynamic constants β1,1H,G , which control simple host-guest ([HG]) association, is crucial in medicine, biology, pharmacy, and chemistry, since the optimum concentration of an effector (i.e., a drug) acting on a receptor is set to 1β1,1H,G . Intermolecular association between charged species in polar solvents, for which water is the archetype, largely obeys this principle. Any deviation from ideality, which alters the speciation in solution, is mastered by the Debye-Hückel theory of ionic atmosphere. Much less is known for related association reactions involving neutral species in non-polar (lipophilic) media such as membranes, bilayers, or organic polymers. Taking the intermolecular association between [La(hfa) dig] guest (hfa=hexafluoroacetylacetonate, dig=2-{2-methoxyethoxy}ethane) and tridentate polyaromatic host receptors L1-L3 in dichloromethane as a proof-of-concept, we show that the progress of the association reactions, as measured by the increase in the mole fraction of occupied sites of the receptors, disrupt the chemical potential of the solvent to such an extent that β1,1H,G may seemingly be shifted by two orders of magnitude, thus leading to erroneous dose-response prescriptions. A simple chemical model, which considers a subset of solvent molecules in surface contact with the partners of the association reaction, restores reliable access to true and interpretable thermodynamic constants. The concomitant emergence of a concentration-dependent corrective parameter reestablishes satisfying dose-dependent response under real conditions. This "complement" to the law of mass action offers a simple method for safely taking care of the non-predictable variations of the activity coefficients of the various partners when host-guest reactions are conducted in non-polar media.

Since its identification as an independent topic after the first world war, the chemistry of

No abstract

Host–guest assembly processes involving neutral partners in solution are usually thought to only involve the chemical reorganization of the solvated species, whereas the bulk solvent behaves as an innocent matrix. However, experimental data collected during titrations of neutral tridentate ligands (orange receptor) with neutral lanthanum transporters (colored bowl) are stubborn as mules because they point that the chemical potential of the solvent is seriously disrupted by the progress of the chemical reaction (vortex). More information can be found in the Full Paper by C. Piguet et al. on page 16787.